1. Vincent ROUBEIX 1 & Françoise CHALIÉ 2
Diatom-inferred paleohydrological changes in lake Abiyata (Ethiopia) at the termination of the African humid period (5.5 cal. kyr BP)
Vincent ROUBEIX 1 & Françoise CHALIÉ 2
1: Irstea, UR RECOVER, AFB-Irstea consortium on lake hydroecology, Aix-en-Provence, France 2 - Aix-Marseille Université, CNRS-UMR 7330, CEREGE UM34, Aix-en-Provence, France
General setting and data used
The lake Ziway-Shalla system
Bathymetry, lake Abiyata; location of core AB95II 2 4 6 8 10
Gulf of Aden 1
How brutal was the termination of the African humid period in central Ethiopia? Was there a transition period?
How can be explained the single conductivity peak ?
Correspondence analysis of core samples between 6.5 and 4.5 kyr BP). There is a clear transition period with a high variability of assemblages between two stable states (1 and 2). The fluctuations along axis F2 suggest a variable climate at the time scale of this period.
Evolution of the relative abundance of the 2 species contributing most to F2 axis. The fluctuations observed in the correspondence analysis are mostly due to high variations in relative abundance of a planktonic species (Rhopalodia gibba) and then a benthic species (Stephanodiscus minutulus) 1 2
Relative abundance (%)
Relative abundance in the sediments of the four diatom species showing the largest variations at the conductivity peak. t0, t1 and t2 refer to just before, at and just after the peak.
Distribution of the 4 species in the conductivity gradient of the modern reference African dataset. The species seem to be sensitive to a conductivity threshold between 1000 and 3000 µS.cm-1.
A gradient forest analysis performed on the modern African dataset reveals the same community threshold which may have a wide ecological significance.
log10 Conductivity (µS/cm)
Conceptual scheme showing how small variations in conductivity around an ecological salinity threshold may produce large variations in diatom community composition and possibly an over-estimation of conductivity change.
Conclusion: The termination of the African humid period in central Ethiopia was preceded by a transition period (<600 yrs) with hydrological variations assigned to climatic fluctuations which may be early warning signals before a climatic regime shift. An ecological salinity threshold may explain the high conductivity peak during this unstable transition period.
European Geosciences Union
General Assembly, 8-13 April 2018